Overview:
This article explains how AutoPIPE Vessel evaluates axial loads related to the f1 and f2 parameters for conical sections in accordance with ASME Section VIII Division 1, Appendices 1-5 and 1-8, and clarifies the software behavior for both vertical and horizontal vessels.
Query:
A user applies an axial force at the small end of a conical section and notices that the calculated values of f1 and f2 remain zero in the design results.
Explanation:
AutoPIPE Vessel considers axial loads per unit circumference at:
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- f1 = Large end of the cone
- f2 = Small end of the cone
However, this calculation is currently supported only for vertical vessels.
For horizontal vessels, axial loads are not considered in the determination of f1 and f2 values. As a result, the entered axial load will not be reflected in these calculations, and the reported values may remain zero.
Important Note
This behavior is a product limitation and is not a software defect.
If support for axial load consideration in horizontal vessels is required, the request should be submitted as an enhancement through the Bentley Ideas Portal for future product evaluation and development.
Frequently Asked Questions (FAQ)
Question 1:
For a vertical vessel, if a positive axial load is entered in the Loads dialog, does it represent a compressive force?
Answer:
A positive axial load entered in the Loads dialog box is interpreted by AutoPIPE Vessel as a downward acting vertical force, similar to a weight load.
Whether this load produces tensile or compressive stress depends on the location being evaluated. In general, the load may create compressive stress at points located:
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- Below the load application point, and
- Above the vessel support junction.
Therefore, a positive axial load does not inherently mean compression everywhere in the vessel; the resulting stress condition depends on the load path and the location under consideration.
Question 2:
Why do the calculated values of f1 and f2 appear negative for positive pressure cases and positive for negative pressure cases?
Answer:
The sign convention for f1 and f2 follows the pressure loading condition:
Internal Pressure
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- Positive values indicate tensile forces.
- Negative values indicate compressive forces.
External Pressure
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- Positive values indicate compressive forces.
- Negative values indicate tensile forces.
When reviewing f1 and f2 results, it is important to interpret the sign based on the applicable pressure condition (internal or external) and the associated stress state.
See Also